The Upper Permian and the Lower Triassic in Kashmir, India

Abstract

It has been known since more than seventy years ago that the fossiliferous Permian-Triassic rocks are well developed around the Vihi plain near Srinagar in Kashmir. It is confirmed that the Upper Permian-Lower Triassic boundary is actually conformable and gradational, and that the basal part of the Lower Triassic beds contains survived Permian-type fossils. The geography and the general geology of Kashmir are briefly introduced, and a history of research on the Permian and the Triassic is given in some detail. The stratigraphy of the beds, not only near the erathem boundary but also belonging to the Upper Permian and the Lower Triassic, is fully described from Guryul ravine and a spur 3 km north of Barus spur. The Permian rocks around Vihi plain are usually classified into the Panjal volcanic rocks, the Gangamopteris Beds (the Lower Gondwana Beds), and the Zewan Formation, in ascending order. The Zewan Formation consists of limestone, sandy limestone, calcareous sandstone, and sandy shale or shale, and is lithologically divisible into four members, A to D, in ascending order at Guryul ravine, and five members, a to e, at a spur 3 km north of Barus. The succeeding Lower Triassic strata are collectively named the Khunamuh Formation in the present paper, of which the basal part belongs to the Permian. The formation is composed mostly of alternations of limestone and black shale, and is subdivided into six members, E to J, at Guryul ravine, and three members, f to h, to the north of Barus, on the basis of the amount of limestone. The Zewan Formation and the lowermost Khunamuh (Unit E1 and Unit f1) are classified into four divisions, I to IV, by characteristic fossil assemblages, although the brachiopod fauna does not change essentially throughout the sequence. Division I corresponding to Member A yields rich foraminifera, bryozoans, and crinoid-stems. Brachiopods are locally concentrated. Colaniella cf. minima, C. cylindrica, and Abadehella cf. coniformis are the characteristic foraminifera which enable to correlate the division with the Lepidolina kumaensis zone in Japan, and the lower Wuchiapingian in south China. It is compared to the Kalabagh Member of the Wargal Formation in the Salt Range by brachiopods and bryozoans. Division II corresponding to Member B is rather poor in organic remains, and it is not ceratin whether it is correlated to the Kalabagh or the Chhidru. It differs from the underlying one in the remarkable decrease of foraminifera and bryozoans due to environmental change. Division III includes Members C and D, and is characterized by a predominance of gastropods and bivalves similar to those of the Upper Chhidru Formation. Cyclolobus walkeri is found from the middle of this division in association with Anchignathodus typicalis and Neogondolella carinata. These fossils strongly suggest the very late Permian (early Dzhulfian, Araksian) age. Division IV coincides with Unit E1 or Unit f1 of the Khunamuh Formation, and is marked by Claraia bioni, n. sp., Etheripecten haydeni, n. sp., and brachiopods survived from the lower division. Conodonts are represented by rare specimens of Anchignathodus typicalis, Neogondolella carinata, and Ellisonia triassica. The division is probably correlated to the uppermost Permian (upper Dzhulfian, Dorashamian or Changhsingian). The Khunamuh Formation is common in ammonoids, bivalves, and conodonts, by which the formation can be divided into several zones, that is, the Otoceras-Glyptophiceras, the Ophiceras, the Paranorites-Vishnuites, the Prionites-Koninckites, and the Owenites-Kashmirites by ammonoids; the Claraia bioni-Etheripecten haydeni, the Eumorphotis benetiana- E. aff. bokharica, the Claraia cf. griesbachi-Eumorphotis multiformis, the Claraia concentrica, the Leptochondrian minima, and the Claraia decidens by bivalves; and the Anchignathodus typicalis, the Neogondolella carinata, the Neospathodus cristagalli, and the N. waageni by conodonts. Among them the Anchignathodus typicalis zone covers the Cyclolobus walkeri horizon of the Zewan up to the Otoceras-Glyptophiceras zone of the Khunamuh crossing over the Permian-Triassic boundary as in the Salt Range and Iran (Abadeh and Julfa regions). The Permian-Triassic boundary is referred to as the base of the Otoceras woodwardi zone taking into the consideration the worldwide recession of the sea and the extinction of the major groups flourished in the late Paleozoic in addition to the faunal changes observed in Kashmir. The boundary in Kashmir is in the lowermost part of the Khunamuh, not at the base but at slightly higher horizon, and does not coincide with the lithological classification. Several Permian species, such as Claraia bioni, Etheripecten haydeni, Marginifera himalayensis, and Pustula sp. are rarely found from the basal part of the Otoceras beds, and are considered to have survived into the beginning of the Triassic. The carbonate layers alternating with argillaceous beds of Member C of the Zewan Foramtion and the Khunamuh are developing in internal sedimentary structures, such as graded bedding, cross and parallel laminations, and convolute structure which suggest the turbidity current origin of these layers, especially in the Khunamuh. Detailed comparison of the sedimentary rocks between the two formations in the field and under the microscope as well, shows that a relatively shallow sea condition during the late Permian rather rapidly changed into the deeper, more off-shore environment at the beginning of the Triassic.